1. Field of the Invention
The present invention relates to an imaging apparatus and an imaging control method, and particularly, to a technique applied to an imaging apparatus of a rolling shutter system.
2. Description of the Related Art
An imaging apparatus has been proposed in which flash emission and exposure timing are matched to prevent in-plane exposure unevenness in a camera with focal plane shutter (Japanese Patent Application Laid-Open No. 2006-64974).
It is known that a reading system in an image apparatus using a CMOS image sensor is a rolling shutter system, in which sequential resetting is performed from the top, and sequential reading is performed.
The rolling shutter system is characterized in that there is a time difference in the exposure timing of the lines as shown in FIG. 26. Therefore, if intense light with short emission period, such as a flash, enters during an exposure period of part of the lines as shown in FIG. 27, areas of the part of the lines are brighter than areas of the other lines. There is a problem that in-plane exposure unevenness occurs as shown in FIG. 28.
Furthermore, there is a time difference in the exposure timing of the lines in the rolling shutter system. Therefore, there is a problem that the image of an object is distorted in case of a moving object.
Japanese Patent Application Laid-Open No. 2006-64974 proposes a camera system in which, the running speed of the back curtain is changed in the camera with focal plane shutter to allow artificial flat emission by a flash device, and the exposure unevenness does not occur in high-speed flash imaging.
Japanese Patent Application Laid-Open No. 2008-252195 proposes an imaging apparatus that can take an image of a moving object without distorting the image even if there is no mechanism for the global shutter.
In the imaging apparatus described in Japanese Patent Application Laid-Open No. 2008-252195, a blank period, in which pixel signals are not read at all, is set in a period from the completion of reading of a pixel signal of one screen to the start of reading of a pixel signal of one screen, and a light emitting diode is lit throughout a certain period in the blank period. The emission from the light emitting diode serves as imaging fill light, and the image of the moving object can be taken without distortion. Furthermore, the emission within the blank period prevents the exposure unevenness caused by the imaging fill light.
Japanese Patent Application Laid-Open No. 2007-6097 proposes a camera in which a live view display is not updated during the irradiation of fill light for distance measurement to thereby prevent highlight clipping of the live view display screen.
Japanese Patent Application Laid-Open No. 2007-49363 proposes a camera in which an artificial highlight clipping image is displayed during the irradiation of fill light for distance measurement to allow the user to visually recognize that the fill light is being irradiated.